Biomedical subjects
W F Mommaerts
Publications and source records attributed to W F Mommaerts.
Trisphosphoinositol as the intra-myonal signal messenger, crucial in excitation-contraction coupling in muscle.
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The enthalpies of ionization of the imidazole group of carnosine and the methylimidazole group of anserine.
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Neural influences on the distribution of troponin I isotypes in the cat.
An immunohistochemical technique was used to study changes in the distribution of fast and slow forms of troponin I (TN-I) in response to alterations in the nerve supply. Hind limb muscles from normal, spinal-isolated, and cordotomized cats, one leg of which had undergone cross innervation between slow (soleus) and fast (flexor hallucis longus, FHL) muscles, were examined. At 8 months after cross innervation of normal soleus by the FHL nerve, the number of fast TN-I-positive cells had increased from 0.26 to 22.1%. At 8 months after cross innervation of normal FHL muscle with the soleus nerve, the number of fast TN-I-positive cells had decreased from 86.5 to 30.5%. The number of intermediate cells staining for both fast and slow TN-I, increased considerably after cross innervation of both soleus and FHL muscles. Spinal isolation by itself had a dramatic effect on the distribution of fast and slow TN-I, converting almost all the originally slow fibers in the FHL and 60.0% of the soleus fibers to fast TN-I-positive cells in 8 months. Cordotomy, in contrast, produced an increase of only 15.6% in the soleus, and did not change the FHL. There was no quantitative difference in the crossed-and uncrossed muscles of spinal isolated cats. In cordotomized cats, cross innervation of the soleus by the FHL nerve resulted in 32.3% fast TN-I-positive cells, with some fiber type grouping. Thus, distribution of fast and slow forms of TN-I changed after each neural manipulation which altered amounts and patterns of muscle contraction and stretch.
[Reflections on muscle research (in commemoration of Prof. A. Katschalsky-Katzir)].
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The origin of concepts regarding contractility, its mechanism, and its control.
The function of the heart is to contract and relax rhythmically so as to propel blood, and the requirements for that function are variable, dependent on the activity of the body. Skeletal muscle also performs variable output tasks but does so by mobilizing a smaller or larger fraction of its motor units. The heart responds in all-or-none manner and must therefore have other means of achieving variable contractile strength. In the first part of this chapter, this will be discussed in a general way, considering mechanisms that heart and muscle have in common. In the second part, we shall then examine properties that are peculiar to the myocardium. The main message of the first part is primarily that much is now known about molecular processes of contraction and of excitation--contraction coupling and that these mechanisms, although subject to specialized modifications, are common to muscle and heart. Of the second part, the main feature is that the variability of excitation--contraction coupling is a major and essential characteristic of the myocardium.
Characterization of myosin heavy chain by cyanogen bromide peptide maps.
Procedures have been developed for the preparation of pure myosin heavy chain (h-myosin) by preparative gel electrophoresis, and for the characterization of h-myosin by cyanogen bromide peptide mapping. Major sources of error are the oxidation of methionine and the proteolytic splitting of the chain during purification. These errors have been eliminated. A peculiar feature is the doubling or quadrupling of a peptide of molecular weight 17 000. The results show structural differences between isomyosins derived from myonal types within the same animal, as well as interspecies differences.
Evidence for a direct action of thyroid hormone in specifying muscle properties.
Thyroidal trophic effects on slow-twitch skeletal muscle properties were compared in normally innervated and denervated soleus of rats maintained at different thyroid states. Hypothyroidism caused fast to slow changes in fiber type composition (99% decrease in proportion of type II fibers), ATPase activities (down 20-30%), myosin light chain pattern (54% less fast light chains), calcium uptake by SR (down 60%), LDH activity (down 11%), and isozyme pattern (9% decrease in M-subunits). Changes of similar magnitude but opposite in direction were induced by thyrotoxicosis. Denervations reversed, to varying degrees, the fast to slow transformations observed in hypothyroidism. However the slow to fast changes found in hyperthyroidism were facilitated rather than inhibited by denervation. These latter results clearly show that the hormone effect can be elicited in the absence of motor innervation. Furthermore, denervation alone caused slow to fast changes in euthyroid muscles. From these results, it is proposed that denervation and dysthyreosis alter muscle properties by independent mechanisms. Our data favor a direct action of thyroid hormone over a neurally mediated mechanism.
The effects of thyroid status on some properties of rat fast-twitch muscle.
The effects of different thyroid states on some histochemical and biochemical properties of fast-twitch muscle were studied using rat extensor digitorum longus (EDL) muscle. This muscle was found to be much less responsive to thyroidal influence than the slow-twitch soleus muscle. In EDL muscles of hypothyroid rats, fast leads to slow conversions were observed in fibre type composition, myosin ATPase activity and light chain pattern, and in the subunit composition of lactate dehydrogenase, while the only significant slow leads to fast conversion observed in thyrotoxicosis was a decrease in the proportion of slow-oxidative fibres. Denervation of the hypothyroid muscle produced the highest degree of fast leads to slow transformation. These findings support the view that denervation and dysthyreosis alter gene expression in muscle by independent mechanisms.
The conversion of some biochemical properties of mammalian skeletal muscles following cross-reinnervation.
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The origin of the tyrosyl circular dichroism of tropomyosin.
1. The near ultraviolet circular dichroism of tropomyosin is due to tyrosine and to disulphide bonds. The optical activity of these chromophores can be distinguished by oxidising and reducing the protein. The circular dichroism due to tyrosine is exceptionally intense and is anomalous in that the shape of the spectrum and the wavelength of the maximum are different from those of the absorption spectrum. 2. The intense tyrosyl circular dichroism and the mismatch between circular dichroism and absorption spectra are likely to be due to tyrosine-tyrosine interactions at distances of less than 8 A. 3. The results are analysed in terms of the coiled coil model for tropomyosin and lead to the conclusion that the tyrosines of one helical subunit interact with those of the other. The in-register alignment of the helical chains, with five tyrosines of one chain opposite those of the other, accounts for the tyrosine-tyrosine interactions. 4. The disulphide circular dichroism of oxidized tropomyosin is intense and is consistent with intra-molecular disulphide bonds between helical subunits which can form in the non-staggered model for tropomyosin.
A temporal dissociation of energy liberation and high energy phosphate splitting during shortening in frog skeletal muscles.
Measurements of the time course of high energy phosphate splitting and energy liberation were performed on rapidly shortening Rana pipiens skeletal muscles. In muscles contracting 30 times against small loads (less the 0.02P), the ratio of explained heat + work (H + W) (calculated from the measured high energy phosphate splitting) to observed H + W (from myothermal and mechanical measurements) was 0.68 +/- 0.08 and is in agreement with results obtained in isometric tetani of R. pipiens skeletal muscle. In lightly afterloaded muscles which were tetanized for 0.6a and whose metabolism was arrested at 3.0 s after the beginning of stimulation, a similar ratio of explained H + W to observed H + W was obtained. However, in identical contractions in which metabolism was arrested at 0.5-0.75 s after the beginning of stimulation, the ratio of explained H + W to observed H + W declined significantly to values ranging from 0.15 to 0.40. These results suggest that rapid shortening at the beginning of contraction induces a delay between energy production and measurable high energy phosphate splitting. This interpretation was tested and confirmed in experiments in which one muscle of a pair contracted isometrically while the other contracted against a small afterload. The afterload and stimulus pattern were arranged so that at the time metabolism was arrested, 0.5 s after the beginning of stimulation, the total energy production by both muscles was the same. Chemical analysis revealed that the isotonically contracting muscle spilt only 25% as much high energy phosphate as did the isometrically contracting muscle.
A survey of the regulatory activity of some phosphorylated and dephosphorylated forms of troponin.
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Activation of phosphorylase in frog muscle as determined by contractile activity.
The state of activation of phosphorylation in muscle has been reinvestigated by combining the extraction procedures of Danforth, Helmreich, and Cori with the low-temperature techniques of this laboratory. In resting frog muscle, the phosphorylase-alpha content is usually below detectability. Upon contractile activity in series of twitches, activation of phosphorylase beta to alpha took place, without activation of phosphorylase beta kinase as defined by the assay procedure. Two different experimental designs were used to examine the relation between phosphorylase activation and the myothermally determined energy turnover per twitch, and these showed, identically, that the enzyme activation is proportional to the energy per twitch.
Chemical energy and cardiac work.
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Current problems in myocardial metabolism.
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The exchange of 18O between water and phosphate compounds in isolated frog sartorius muscle under conditions of negative work.
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Energetics of shortening muscles in twitches and tetanic contractions. II. Force-determined shortening heat.
The extra heat liberation accompanying muscular shortening, the force-determined shortening heat, is defined as the difference between the heat produced when shortening occurs and that produced in an isometric contraction developing the same amount of force and performing the same amount of internal work. Based on this definition, the initial energy production in twitches and tetanic contractions (E) is given by E = A + f (P, t) + alpha(F)x + W, where A is the activation heat, f(P, t), the tension-related heat (a heat production associated with the development and maintenance of tension), alpha(F)x, the force-determined shortening heat, and W, the external work. It is demonstrated that this equation accurately accounts for the time-course of heat evolution and the total initial energy production in both twitches and tetani at 0 degrees C. The force-determined shortening heat is liberated, during shortening, in direct proportion to (a) the distance shortened, and (b) the force against which shortening occurs. The normalized value of the force-determined shortening heat coefficient, alpha(F)/P(o), is the same in both the twitch and the tetanus. Finally, this formulation of the muscle's energy production also accounts for the total energy production in afterload isotonic twitches at 20 degrees C, where a Fenn effect is not demonstrable.